System Integration Module
MOTOROLA
MC68307 USER’S MANUAL
5-25
5.2.1.4 SYSTEM CONTROL REGISTER BITS DESCRIPTION. The following paragraphs
describe the system control register bits.
ADCE—Address Decode Conflict Enable
This bit is used to enable or disable the automatic bus error condition (BERR) which can
be raised when the chip select logic reports an address conflict.
0 = BERR is not asserted by a conflict in the chip select logic when two or more chip
select lines are programmed to overlap the same area.
1 = BERR is asserted by a conflict in the chip select logic when two or more chip select
lines are programmed to overlap the same area.
After cold reset, this bit defaults to zero, so the automatic bus error is disabled.
NOTE
When the chip select logic reports an address conflict, the ADC
bit is set, regardless of the value of ADCE bit.
WPVE—Write-Protect Violation Enable
This bit is used to enable or disable the automatic bus error condition (BERR asserted)
which can be raised when the chip select logic reports a write-protect violation.
0 = BERR is not asserted when a write protect violation occurs.
1 = BERR is asserted when a write protect violation occurs.
After cold reset, this bit defaults to zero, so the automatic bus error is disabled.
NOTE
When the chip select logic reports a write-protect violation, the
WPV bit is set, regardless of the value of the WPVE bit.
EPCS—Enable Peripheral Chip Selects
This bit enables or disables the expansion of chip select 2 and its output pin into 4 individ-
0 = The CS2/CS2A output pin functions as a generic chip select, CS2. The CS2B/PA0,
CS2C/PA1, and CS2D/PA2 pins function as general-purpose input/output PA0,
PA1 and PA2, subject to correct programming of the PACNT.
1 = The CS2/CS2A output pin functions as a the first of four peripheral chip select out-
puts, CS2A. The CS2B/PA0, CS2C/PA1, and CS2D/PA2 pins function as the other
three peripheral chip select outputs, CS2B, CS2C, CS2D, subject to correct pro-
gramming of the PACNT. The block size for this chip select should be 64-Kbytes;
each output signal selects a 16-Kbyte range within the block. If less than four pe-
ripheral chip selects are required, they can be individually enabled/disabled in
PACNT.